diff --git a/Directories-and-Files.md b/Directories-and-Files.md
index 42f8c71..5b8ad8e 100644
--- a/Directories-and-Files.md
+++ b/Directories-and-Files.md
@@ -76,14 +76,14 @@ For directory renaming, it will be O(N) operations, with N as the number of file
 
 The Filer Store persists all file metadata and directory information.
 
-| Filer Store Name | Lookup | number of entries in a folder | Scalability | Note |
-| ---------------- | -- | -- | -- | -- |
-| memory       | O(1)   | limited by memory | Local, Fast                | for testing only, no persistent storage |
-| LevelDB      | O(logN)| unlimited | Local, Very Fast               | Default, fairly scalable |
-| Redis        | O(1)   | limited   | Local or Distributed, Fastest  | one directory's sub file names are stored in one key~value entry |
-| Cassandra    | O(logN)| unlimited | Local or Distributed, Very Fast|                   |
-| MySql        | O(logN)| unlimited | Local or Distributed, Fast     | Easy to manage, export |
-| Postgres     | O(logN)| unlimited | Local or Distributed, Fast     | Easy to manage, export |
+| Filer Store Name | Lookup | number of entries in a folder | Scalability | TTL | Note |
+| ---------------- | -- | -- | -- | -- | -- |
+| memory       | O(1)   | limited by memory | Local, Fast                |  | for testing only, no persistent storage |
+| LevelDB      | O(logN)| unlimited | Local, Very Fast               |  | Default, fairly scalable |
+| Redis        | O(1)   | limited   | Local or Distributed, Fastest  |Yes| one directory's sub file names are stored in one key~value entry |
+| Cassandra    | O(logN)| unlimited | Local or Distributed, Very Fast|Yes|                |
+| MySql        | O(logN)| unlimited | Local or Distributed, Fast     | | Easy to manage, export |
+| Postgres     | O(logN)| unlimited | Local or Distributed, Fast     | | Easy to manage, export |
 
 #### Switching between different Stores
 It is easy to switch between different filer stores (except memory store).